I have a female character in her early twenties. How realistic would it be for her to be skilled (enough to hold her own against larger opponents) in hand to hand combat in under two years? If not, what would be realistic for her to master?

It’s realistic, sort of. There’s a few minor issues that don’t
really fit together here, making it (at least seem) unrealistic as written.

Practical martial arts training intended to put someone into
combat lasts far less than two years. You can learn effective hand to hand
techniques that you can then apply in combat in an eight week course. If you’re
coming out of the military or from a police background, your hand to hand
training took, at most, a couple months. Then you go back every six months to a
year, and update it, meaning you learn what others have developed to counter
your training, and how to deal with their counters.

Practical training isn’t so much about spending years
learning how to fight, as checking in often enough to see what’s changed. When
you’re dealing with untrained opponents, it really doesn’t matter. Most people
haven’t been in a fight since high school, and even basic police adapted Judo
from the 70s will take them down.

As we’ve said many
times before, most martial arts apply to larger foes without missing a
beat. This is especially true of the adapted Judo/Jujitsu which forms the core
of most American police and self-defense forms. This may be a difficult concept
to wrap your head around, but it is far
easier to put an opponent on the ground when they’re a foot taller, and a
hundred pounds heavier, than the other way around.

Depending on how zealous they are about keeping their
training up to date, someone who underwent training two years ago will have
gone back four to six times, to update. They may have also elected to retake
their training just to, “brush up.” Either way, we’re not talking about someone
dedicating a lot of their life to this.

That said, if you’re talking about someone who signed up at
a Dojo, and has been taking weekly classes, there’s no way to know what they’re
trained to deal with. Some recreational schools will get into practical
applications for their martial art, and offer it as an optional advanced class
for their students. At that point, it’s entirely dependent on her instructor if
she gets in (as an adult, these would probably be open to her if she wanted).
It’s also, depressingly common for a martial arts school to offer, “self-defense,”
classes that are just their normal curriculum with a different advertising
hook. A class like this will not prepare your character for a self-defense
situation.

For reference: If you’re taking a self defense class, and
the discussion doesn’t include a serious discussion on situational awareness,
and/or your instructor puts a lot of faith in your ability to overcome via
superior force then you’re probably in the wrong place. Real self-defense
training focuses on creating an opening so you can retreat to safety (if
possible). It’s concerned with your ability to escape the situation and
survive, not your ability to win a fight. Sticking around and dealing with an
assailant is something you would only want to consider very situationally.

Also, in case it’s not clear, when I’m talking about Police
adapted Judo, it is not the same
martial art as Judo. It was derived from Judo after the Second World War, and
the modern martial art still shares some techniques, but there have been
substantial modifications to it, in order to produce something functional for
combat. Judo itself is intended to be a sport martial art, and not something you’d
take into combat.

There’s also no way to know exactly how fast the school
moves its students through, and how quickly your character would advance. These
are all dependant on human interactions and how quickly they learn and
internalize techniques. In a more traditional school, two years is not a lot of
time, but a modern Dojo may move a lot faster. It all comes down to the
instructor’s preferences.

That said, recreational martial artists are not (usually)
trained for combat. There’s a fundamental disconnect between how practical
martial artists approach techniques, and how recreational ones do. They’re
often studying the exact same techniques, but with different goals in mind. The
recreational martial artist is learning to perform it, the practical one is
learning to apply it. This might not sound important, or could come across as
irrelevant trivia, it’s not. This is a large part of why practical training is
so much faster. You’re learning how to do things to your opponent, not how to perform
the techniques correctly.

A character who’s spent two years taking a martial art in a
recreational capacity, may be able to handle an untrained opponent (it’s
actually, fairly likely, assuming they don’t make any critical mistakes, which
is also quite possible), but may face serious issues dealing with a trained
opponent (this will depend entirely on what each character’s training focused
on). Someone who has trained with a practical focus will be able to take on an
untrained opponent (assuming they don’t make any major mistakes or misjudge the
situation). Ironically, they’re also far more likely to attempt to avoid direct
confrontation, and try to defuse the situation non-violently, than a trained
recreational martial artist would.

So, your character’s been training for two years, and you want
to know what she can tackle. If she was simply going to a Dojo twice a week,
that’s not combat ready. That may not even be combat ready, if the Dojo’s “self-defense”
class was run by the same instructors who believe their decade training in a
sport martial art is good enough for “the streets.”

If your character’s been training with a cop, or ex-military,
relative/friend/rando, or been in police sponsored self-defense classes, then
two years is more than enough time to be able to deal with an opponent.

There’s an unrelated issue that Michi would be irked if I
didn’t bring up. (We both started typing up radically different responses to
this question.) Mastery a term that gets tossed around a lot in fiction. In
martial arts, two years isn’t long enough to master anything. It’s not enough time to master the basics, it’s certainly
not enough time to master advanced techniques. Mastery reflects a very high
baseline of skill, and can easily take decades of dedicated training. A
character can become proficient in elements of a martial art fairly quickly.
That is to say, they can perform them correctly, and present a solid (or
effective) technique. But, mastery, in this context, is a much higher bar to
hit, and not one a character will reach within the first few years of starting
a martial art.

There’s one last thing, “hold her own,” is a very difficult goal.
Unarmed combat doesn’t tend to equalize out like this. You either win, lose, or
wear each other out in fairly short order. Combat is extremely tiring, it’s
part of why real self-defense tends to focus on creating an opening and
escaping. Sticking around and trying to win a fight through attrition is a losing
proposition for nearly everyone. Getting a good clean shot in on someone is
usually enough to create the distance you need to escape. It’s not, “winning,”
but, if all you need to do is retreat, that’s all you need. If you’re going to
stick around, then the goal is to take your opponent down quickly and
decisively. Unarmed combat doesn’t allow for protracted dueling the way Wuxia
films present it.